1. Field of the Invention
The present invention is directed to vibratory screens, to filtering screens, to such screens that are generally flat or that are not flat, to devices with such screens, and to shale shakers with such screens, and to shakers for separating particles.
2. Description of Related Art
The need for solids control in drilling mud used in hydrocarbon well drilling is well known in the prior art. Drilling mud, typically a mixture of clay and water and various additives, is pumped down through a hollow drill string (pipe, drill collar, bit, etc.) into a well being drilled and exits through holes in a drillbit. The mud picks up cuttings (rock) and other solids from the well and carries them upwardly away from the bit and out of the well in a space between the well walls and the drill string. At the top of the well, the solids-laden mud is discharged over a shale shaker, a device which typically has a series of screens arranged in tiered or flat disposition with respect to each other. The prior art discloses a wide variety of vibrating screens, devices which use them, shale shakers, and screens for shale shakers. The screens catch and remove solids from the mud as the mud passes through them. If drilled solids are not removed from the mud used during the drilling operation, recirculation of the drilled solids can create weight, viscosity, and gel problems in the mud, as well as increasing wear on mud pumps and other mechanical equipment used for drilling.
In some shale shakers a fine screen cloth is used with the vibrating screen. The screen may have two or more overlying layers of screen cloth. The prior art discloses that the layers may be bonded together; and that a support, supports, or a perforated or apertured plate may be used beneath the screen or screens. The frame of the vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by a vibrating mechanism, e.g. an unbalanced weight on a rotating shaft connected to the frame. Each screen may be vibrated by vibratory equipment to create a flow of trapped solids on top surfaces of the screen for removal and disposal of solids. The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.
Many screens used with shale shakers are flat or nearly flat (i.e. substantially two-dimensional). Other screens, due to corrugated, depressed, or raised surfaces are three-dimensional. U.S. Pat. Nos. 5,417,793; 5,417,858; and 5,417,859 disclose non-flat screens for use with shale shakers. These screens have a lower planar apertured plate with a multiplicity of spaced-apart apertures or openings therethrough. Undersides of troughs of undulating screening material are bonded to the apertured plate. Such screens present a variety of problems, deficiencies, and disadvantages, including: decreased flow area due to area occluded by solid parts of the apertured plate; necessity to either purchase relatively expensive apertured plate or provide for in-house perforating of a solid plate; plate weight increases wear on parts such as rubber screen supports or cushions and can inhibit required vibration; large plate surface area requires relatively large amount of bonding means for bonding screens to the plate; and a finished screen which is relatively heavy increases handling problems, hazards, and cost of shipping.
Vibrating screens have been employed for many years to separate particles in a wide array of industrial applications. One common application of vibrating screens is in drilling operations to separate particles suspended in drilling fluids. The screens are generally flat and are mounted generally horizontally on a vibrating mechanism or shaker that imparts either a rapidly reciprocating linear, elliptical or circular motion to the screen. Material from which particles are to be separated is poured onto a back end of the vibrating screen, usually from a pan mounted above the screen. The material generally flows toward the front end of the screen. Large particles are unable to move through the screen remaining on top of the screen and moving toward the front of the screen where they are collected. The smaller particles and fluid flows through the screen and collects in a pan beneath the screen.
A vibrating screen may be formed from one or more layers of wire mesh. Wire mesh is generally described with reference to the diameter of the wires from which it is woven, the number wires per unit length (called a mesh count) and the shape or size of the openings between wires. Wire mesh comes in various grades. xe2x80x9cMarketxe2x80x9d grade mesh generally has wires of relative large diameter. xe2x80x9cMillxe2x80x9d grade has comparatively smaller diameter wires and xe2x80x9cbolting clothxe2x80x9d has the smallest diameter wire. The type of mesh chosen depends on the application. Smaller diameter wires have less surface and thus less drag, resulting in greater flow rates. Smaller diameter wires also result, for a given opening size, in a larger percentage of open area over the total area of the screen, thus allowing greater flow rates and increased capacity. However, screens of bolting cloth tears more easily than market or mill grade screens, especially when used in harsh conditions such as drilling and mining operations. The smaller diameter wires tend to have less tensile strength and break more easily, and the finer mesh also tends not to retain its shape well.
Most meshes suffer from what is termed as xe2x80x9cnear sized particle blinding. During vibration, wires separate enough to allow particles of substantially the same size or slightly larger than the openings to fall between the wires and become lodged, thus xe2x80x9cblindingxe2x80x9d the openings of the screen and reducing capacity of the screen. If a particle becomes lodged when the wires are at a maximum distance apart, it is almost impossible to dislodge the particle. Sometimes, however, wires will subsequently separate further to release the lodged particle. Unfortunately, some wire mesh, especially bolting cloth, is tensioned. Tensioning restricts movement of the wires. Restricting movement assists in holding the shape of the wire mesh, keeping the size of the openings consistent to create a more consistent or finer xe2x80x9ccutting pointxe2x80x9d and reducing abrasion from wires rubbing against each other. However, restricted movement of the wires reduces the probability that, once a near sized particle becomes stuck, the wires will subsequently separate to allow the particle to pass. Use of smaller diameter wires, with smaller profiles, helps to reduce blinding. With a smaller diameter wire, a particle is less likely to become lodged midway through the opening.
Multiple layers of mesh may be used to alleviate blinding. U.S. Pat. No. 4,033,865, describes layering two meshes in a manner that results in at least one wire of the lower of the two meshes bisecting each opening in the upper mesh. The openings in each mesh are at least twice as wide as the diameters of the wires and the lower mesh has openings the same size as or slightly larger than the openings in the upper mesh. The lower mesh, when held tightly against the upper mesh, prevents particles from migrating far enough into an opening in the upper mesh to be trapped. Some relative movement of the layers also helps to dislodge particles caught in the upper layer. The two-layer arrangement has the further benefit of a finer xe2x80x9ccutting point,xe2x80x9d allowing smaller particles to be separated out. A third xe2x80x9cbackingxe2x80x9d layer of relatively coarse, mill grade mesh is often used to carry most of the load on the screen and to increase the tensile strength of the screen.
Another problem faced in most applications is the tearing of the screen. The problem can be especially acute in heavy duty applications such as drilling and mining. A torn screen must be replaced or repaired. To facilitate repair, the screen layers are bonded to a rigid or semi-rigid support panel that has a pattern of large openings, forming on the screen a plurality of small cells of wire mesh. When a tear occurs in the screen, the mesh remaining within the cell in which the tear occurred is cut out and the cell is plugged. The capacity of the screen is diminished but its life is extended. Typically, several cells of a screen can be repaired before its capacity drops far enough to require replacement. Unfortunately, bonding the screen to the support panel further restricts relative movement of the layers and the wires in each mesh layer, thus compounding the problem of blinding.
Blinding and tearing of the screens reduce the capacity of the screen continually through its useful life. Although capacity can be increased by increasing the total area the screens, the size of the screen is limited in most applications, such as on drilling rigs, especially those on offshore platforms. There has thus been generally a trade-off between capacity, longevity, repairability and resistance to blinding of the screens.
There is a need for a supported (either non-flat or flat) screen which is consumable, efficient and cost-effective, yet readily and inexpensively made, easy to handle, and relatively inexpensive to transport.
The present invention discloses, in certain embodiments, a screen for vibrating screen apparatus. The screen has one or more upper layers of screen, screen cloth, and/or mesh. If more than one layer is used, they may be bonded together at discrete points, at discrete areas, or over their entire surface. The layer or layers are mounted on frame apparatus which may include a id side support on each of two spaced apart sides of the layer(s), or may include a full four sided screen frame. A strip or strips of support material (e.g. flat steel, aluminum or plastic stripsxe2x80x94of any width, but in certain preferred embodiments ranging between a half inch to three inches in width; and of any thickness, but in certain preferred embodiments ranging between one-thirty second and one-eighth inches thick, or rods of these materials with a diameter between one-thirty second and one-eighth inches; any screen may use strips made from different materials, e.g. cross-strips of plastic and end strips of steel, or vice versa) are secured across two or more frame sides. With respect to a two sided frame wherein the two sides are parallel and spaced apart, a strip or strips may be, according to this invention, disposed parallel to the two sides; and, if more than one strip is used, spaced apart across the area of the layer or layers. It is also within the scope of this invention to use a strip or strips which are disposed in a manner non-parallel to the two sides. In one aspect such non-parallel strips may extend diagonally from one end of one side of the frame, across the layer or layers, to a diagonally opposite end of the other side. In another aspect such a strip may extend from any point of a frame side to any point on a non-framed side of the layer or layers. Any such strip (or rod) may be bonded, sintered, welded or otherwise secured (herein referred to collectivley as xe2x80x9cbondedxe2x80x9d) at any point to the layer or layers; at substantially every point of contact between the strip(s) and the layer(s); or at selected intermediate contact points.
In certain embodiments a screen assembly for a vibratory separator is provided that has a corrugated support plate having a plurality of alternating raised portions and lower portions, the corrugated support plate having a plurality of spaced apart openings therethrough, a screen frame with a first pair of spaced apart first sides and a second pair of spaced apart second sides, the first sides spaced apart by the second sides and connected thereto, the frame having a plurality of spaced apart support strips extending beneath the corrugated support plate, each support strip independent of and not connected to the other support strips along its length, each support strip having two spaced apart ends each connected to a spaced apart side of the frame and to which the corrugated support plate is secured. Such a screen assembly may, optionally, have at least one projecting portion on each support strip for reception within a raised portion of the corrugated support plate, and screening material on the corrugated support plate.
In certain embodiments such a strip (or strips) is used with an undulating three-dimensional layer or layers of screen, screen cloth, screen mesh, or some combination thereof (either non-bonded layers or bonded layers if multiple layers are present). If the undulating layer(s) present certain downwardly projecting areas, e.g. troughs between valleys, some or all of the troughs may, within the scope of this invention, be bonded to the strip(s) or portions thereof, and all or only a portion of a trough may be bonded to the strip(s).
Certain prior art shaker screens have a frame side with an in-turned edge w facilitates hooking of the screen, e.g. to a vibrating basket. In one embodiment of the present invention a strip as described above extending between two frame sides also extends into and becomes this in-turned hooked edge. In another aspect a strip is secured to a portion of a hook. To inhibit or prevent fluid leakage at the hook/strip interface, a steel strip may be welded to a metal hook (or a non-metal strip may be bonded to a metal or non-metal hook). In one aspect typical frame sides are not used and only a series of strips with hook edges support the screening material and provide for its mounting to a shale shaker.
In other embodiments in which two frame sides are used, a support strips at opposite ends of the frame sides may also serve as end members across the layer(s) ends which do not have frame sides. In one aspect such strips are emplaced at the leading and trailing edges of the layers.
In embodiments of this invention in which the layer (or layers) are non-flat (e.g. undulating) and there is some sort of extended depressed or lower areas on or across the layers which provide a generally lower path for fluid moving on part of or all the way across a screen, the strip or strips according to this invention may be placed beneath the layer or layers at any desired angle to the direction of flow of the fluid across the screen. Also, in those cases in which the entire screen surface has undulations in a same general direction, the screen may be disposed so that fluid flows across the screen either generally in the same direction as the undulations or transverse to such a direction. In either case, a strip or strips beneath the layer(s) may be in the direction of flow or transverse to it.
In one aspect the strips (or rods) described above have one or more projecting portions formed integrally thereof or secured thereto which project into troughs or areas of the layer(s). Such projecting portions may be shaped and configured to mate with the shape of a hill, valley, trough or indented area; may be bonded to the layer(s) at such areas; may be bonded only to the sides of such areas and not to the uppermost portion of a top portion thereof; or may be adjacent such areas without bonding thereto. If there is a series of parallel troughs or a plurality of adjacent indented areas, such projections may be provided in all such troughs or areas; in only on such trough or area; in troughs or areas only adjacent frame sides; or in only middle troughs or areas. It is within the scope of this invention in embodiments in which the screen has a series of parallel troughs, to use alternating flat strips and strips with one or more projections as described above. It is also within the scope of this invention to use non-flat strips which have a shape that corresponds to the series of troughs, e.g. with undulating layer(s), a corresponding undulating strip is used. Such strips may be used instead of or in combination with flat strips as previously described. Any strip herein may have holes through it to facilitate fluid flow. In one aspect any strip, combination of strips, or pattern of strips disclosed herein may be used with a generally flat (xe2x80x9ctwo-dimensionalxe2x80x9d) screen. In any screen disclosed herein the screening material may be sintered to itself, individual screen wires may be sintered to each other, one or more layers of screen material, cloth, mesh, or screen may be sintered to each other; and any screen material may be sintered to any strip disclosed herein, either entirely along its length or at selected points or areas therealong.
The present invention, in one embodiment includes a shale shaker with a frame; a xe2x80x9cbasketxe2x80x9d or screen mounting apparatus; one or more screens as described above and below; and basket vibrating apparatus.
It is within the scope of this invention to provide a screen as disclosed in U.S. Pat. Nos. 5,417,793; 5,417,858; and 5,417,859, but to delete the apertured plate required by these patents and to use instead a coarse mesh or a coarse flexible mesh. In certain preferred embodiments this mesh ranges in size between a 1 mesh to a 3 mesh, with a 2 mesh used in one particular embodiment. It is within the scope of this invention to use any strip, combination of strips, strip member, or pattern of strips in place of the apertured plate required by the three listed patents. It is within the scope of this invention to use any strip or strips disclosed herein in- combination with the apertured plate required by the three listed patents.
The invention, in certain embodiments, discloses a screen for a vibrating separator or shaker that has increased capacity without an increase in overall dimensions. It furthermore accommodates desirable attributes such as resistance to blinding, repairability and longevity. The screen, substantially horizontal when placed on a separator for operation, is formed from one or more layers of mesh. The one or more layers of mesh are formed into an alternating series of ridges and channels lying substantially within the plane of the screen. The ridges increase the surface area of the screen without increasing the overall dimensions of the screen, thus improving flow capacity. Additionally, particles tend to drop into the channels, leaving the tops of the ridges exposed to fluids for relatively unimpeded flow through the screen that further improves flow rates. Furthermore, the ridges and channels tend to assist in evenly distributing separated particles across the screen. Uneven distribution, due to for example rolling of the screen from side to side when used on offshore platforms, degrades flow capacity of the screen.
In accordance with another aspect of the invention, the wire mesh is bonded to a rigid or semi-rigid panel having an array of openings that are very large as compared to those of the mesh. The support panel is formed with or bent into a series of alternating ridges and channels to create the ridges and channels in the wire mesh when it is bonded to the panel. The openings in the panel create, in effect, a plurality of individual screen cells when the wire mesh is bonded to the panel around each opening. When a portion of wire mesh fails or is torn within a cell, the screen is repaired by cutting the remaining mesh from the cell opening and plugging the cell opening with a solid piece of material.
In accordance with another aspect of the invention, the ridges and channels of the panel have substantially flat surfaces on which the openings are located. A substantially planar opening allows a flat plug to be inserted into the opening for improved fit and sealing. The plug is preferably formed with an edge that facilitates insertion into opening and into which the edge of the cell opening snugly fits, making a repair quick and easy.
In accordance with another aspect of the invention, the ridges have a generally triangular cross section. In a preferred embodiment, the ridges are formed from two surfaces in a triangular configuration and the channel is formed from a flat bottom surface extending between the ridges. This geometry tends to maximize effective or useful surface area of the screen, especially if flat surfaces are used on the ridge to facilitate repair. During normal operation of the separator or shaker, most of the particles fall into the channel and the material to be separated tends to flow through the screen along the sides of the ridges and the bottom of the channel. A generally triangular configuration of the ridge tends to expose greater screen area to the flow and to minimize the amount of area on top of the ridge that tends not to be exposed to material flow.
In another aspect a screen according to the present invention has a lower perforated corrugated plate with a plurality of triangular apertures or openings forming the perforations through the plate. In one aspect the triangles are congruent, of similar size, and are arrayed side-to-side across the plate. In certain aspects when a corrugated plate is used, no plastic grid is placed or used between screens or meshes or between a plate and screening material. The mesh, meshes, screen, screens, or screening material(s) are secured on the plate directly with the use of adhesive on the plate, e.g. but not limited to powder adhesive, without the use of a plastic or adhesive grid. Alternatively such a grid may be used. In certain aspects in which a corrugated perforated plate is used, the screen, mesh or screening material does not contact a strip or multiple strips disposed beneath the plate. In one aspect a corrugated perforated plate is secured to a frame comprised of sides. In another aspect strips as described herein are used with such a frame for certain embodiments. In such a device screening material or mesh secured to the corrugated perforated plate does not contact or bond to the strip/frame assembly.
The present invention discloses, in certain aspects, methods for making screens and screen assemblies as disclosed herein for a vibratory separator, the method including placing at least two layers (in some cases two, three or four layers) of screening material adjacent one another one on top of the other, introducing an amount of glue to the at least two layers of screening material for adhering at least portions of them together, the amount of glue introduced to the at least two layers of screening material from a roller with a patterned surface thereon so that the amount of glue is introduced to the at least two layers of screening material in a pattern corresponding to a pattern of the patterned surface of the roller, the roller rotatably mounted adjacent the screening material. In certain aspects, grooves or recesses are provided in the raised portions or areas of the pattern rollers to create a raised bead of glue.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, non-obvious methods for making screens and screen assemblies; screen assemblies; screen assemblies with one or more lower coarse screen members and one or more upper fine screen members; such screens with one or more bottom strip members, support strips or rods; such screen assemblies in which screening material of adjacent screens is fused together with plastic; and shale shakers or vibratory separators with any such screen assemblies;
Such screens or screen assemblies made with a gluing system that has a pattern roller for creating a desired pattern of glue on a screen or mesh, or combination thereof and which overcome the problems, limitations and disadvantages of prior art screens;
Such a screen or screen assembly with a top most coarse screen or coarse screen portion; and
A shale shaker or vibratory separator with one or more such screens or screen assemblies.
The present invention recognizes and addresses the previously-mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one of skill in this art who has the benefits of this invention""s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent""s object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.